Solvent recovery from photolithography waste using cellulose ultrafiltration membranes

2021-8
Savaş Alkan, Aygen
Cellulose flat sheet ultrafiltration membranes were fabricated for the investigation of their separation performance in Organic Solvent Ultrafiltration (OSU) applications and for the solvent recovery from photolithography wastes. Firstly, cellulose acetate membranes were produced and then, these were converted into cellulose membranes via alkaline hydrolysis. The membranes were cast from polymer solutions containing cellulose acetate as polymer with 20-30% concentration range, dimethyl sulfoxide (DMSO) as solvent, acetone as co-solvent and polyethylene glycol (PEG) as pore former agent. Before use in photolithography waste purification, performance tuning was carried out by changing the polymer, co-solvent, pore former composition; coagulation bath temperature and applying the process of annealing for the main aim of obtaining membranes having high rejection performance accompanying a reasonable permeance. The separation performance of the membranes was tested with the molecular weight cut-off tests and the MWCO tests were firstly done in water. Then, the change in MWCO performance in different solvents was investigated in DMSO and methanol. In MWCO tests, PEG probes with different molecular weights were used for the filtration and Gel Permeation Chromatography (GPC) was used for the analysis. In MWCO tests performed in water, the obtained MWCO range with different membranes was 3-10 kDa. On the other hand, the MWCO tests performed in DMSO, water and methanol for the comparison resulted in 1.3, 3 and 5 kDa. Photolithography is a process widely used in the fabrication of microelectronic devices and it requires high purity metal-free solvents for the process steps to prevent short-circuit failures. In the study, the mimic of developer bath solution with propylene glycol monomethyl ether acetate (PGMEA) consisting of 0.5-2.5 g/L SU-8 photoresist were firstly prepared and filtered via two-stage filtration by the cellulose ultrafiltration membranes. At the end, 91% and 80% SU-8 rejection values were obtained for the first and second filtration stages, respectively. Then, the permeate mixture of two-stage filtrations were tested in photolithography and the pattern results of recycled PGMEA were compared with the pattern of the photolithography applied with fresh PGMEA. As a result, the obtained pattern imprinted via recycled solvent was promising and so, a critical outcome was obtained from cost-efficiency, sustainability and circular economy aspects for the large-scale applications in the microelectronics industry.

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Citation Formats
A. Savaş Alkan, “Solvent recovery from photolithography waste using cellulose ultrafiltration membranes,” M.S. - Master of Science, Middle East Technical University, 2021.